Happy to share, Excel Online now supporting the ability to Select All cells in a range, a table, or sheet; by using Ctrl+A or by clicking the triangle at the top left corner. You are welcome to try it and provide us feedback through the service (File → Help → Provide feedback to Microsoft)

It can help change the size of the boxes and you'll be able to make pixel art. This is a feature on other computers but not for chrome. I'd also recommend that you can zoom in and out on the boxes. This is also a feature shown on other computers. Thank you!